Document map DOM elements

src/ol/map.js

@@ -139,6 +139,15 @@ ol.MapProperty = {
  * The above snippet creates a map with a MapQuest OSM layer on a 2D view and
  * renders it to a DOM element with the id `map`.
  *
+ * The constructor places a viewport container (with CSS class name
+ * `ol-viewport`) in the target element (see `getViewport()`), and then two
+ * further elements within the viewport: one with CSS class name
+ * `ol-overlaycontainer-stopevent` for controls and some overlays, and one with
+ * CSS class name `ol-overlaycontainer` for other overlays (see the `stopEvent`
+ * option of {@link ol.Overlay} for the difference). The map itself is placed in
+ * a further element within the viewport, either DOM or Canvas, depending on the
+ * renderer.
+ *
  * @constructor
  * @extends {ol.Object}
  * @param {olx.MapOptions} options Map options.